Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session G29: Turbulence: Jets & Shear FlowsShear layer Turbulence
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Chair: Jon Baltzer, Los Alamos National Laboratory Room: 205 |
Monday, November 20, 2017 10:35AM - 10:48AM |
G29.00001: A parametric investigation of pressurized spray dispersion using laser-induced phosphorescence Herman Clercx, Nico Dam, Willem van de Water, Dennis van der Voort When a high-speed liquid jet exits the nozzle, it breaks up into a cloud of small droplets surrounding the diminishing liquid core, called a spray. The understanding of breakup and dispersion of these sprays has been an experimental and numerical challenge for decades. The large optical density, small scales, and high velocities, result in a small amount of information on the droplet movement in a Lagrangian sense. Using laser-induced phosphorescence (LIP), we can determine the quantitative spreading of a (small) pre-defined spray volume, a direct measure of the spray dispersion. Using a dedicated spray vessel, pressurized up to ambient pressures of 2 MPa (20 bar), this work investigates the change of both radial and axial dispersion of a heptane and water spray through a wide range of parameters. By investigating the dispersion as a function of Reynolds number, Weber number, liquid properties, ambient density, and the spray velocity, indication of the parameters that strongly affect spray dispersion are given. We will discuss the parameters that affect the dispersion, as well as the fundamental differences between spray dispersion and commonly used spray angles. [Preview Abstract] |
Monday, November 20, 2017 10:48AM - 11:01AM |
G29.00002: Kinematics of the interface in the near field of homogeneous and immiscible turbulent jets Eric Ibarra, Franklin Shaffer, Omer Savas The near field interfaces of turbulent discharges carry clues that can help determine overall discharge rate. The work being presented here concentrates on characterization of the turbulent features visible at the interface. The analysis focuses on utilizing images of the discharge to estimate an interface length scale using correlations along the axis of the discharge. Length scales akin to the Taylor scale show monotonic behavior soon after the discharge location. An analysis of the curvature spectra of the features is also investigated; this is accomplished through the segmentation of a continuous jet into curves that are parametrically represented to evaluate their curvatures. The interface of immiscible jets consists predominately of droplets and ligaments; the length scales along with their dynamics of these structures are explored. These techniques were used to investigate homogeneous water jets, ranging from $Re \sim 4,500-50,000$, and silicon oil jets in water, ranging from $Re \sim 3,500-27,000$. [Preview Abstract] |
Monday, November 20, 2017 11:01AM - 11:14AM |
G29.00003: ABSTRACT WITHDRAWN |
Monday, November 20, 2017 11:14AM - 11:27AM |
G29.00004: Effects of the shear layer growth rate on the supersonic jet noise Yuta Ozawa, Taku Nonomura, Akira Oyama, Hiroya Mamori, Naoya Fukushima, Makoto Yamamoto Strong acoustic waves emitted from rocket plume might damage to rocket payloads because their payloads consist of fragile structure. Therefore, understanding and prediction of acoustic wave generation are of importance not only in science, but also in engineering. The present study makes experiments of a supersonic jet flow at the Mach number of 2.0 and investigates a relationship between growth rate of a shear layer and noise generation of the supersonic jet. We conducted particle image velocimetry (PIV) and acoustic measurements for three different shaped nozzles. These nozzles were employed to control the condition of a shear layer of the supersonic jet flow. We applied single-pixel ensemble correlation method (Westerweel et al., 2004) for the PIV images to obtain high-resolution averaged velocity profiles. This correlation method enabled us to obtain detailed data of the shear layer. For all cases, acoustic measurements clearly shows the noise source position at the end of a potential core of the jet. In the case where laminar to turbulent transition occurred in the shear layer, the sound pressure level increased by 4 dB at the maximum. [Preview Abstract] |
Monday, November 20, 2017 11:27AM - 11:40AM |
G29.00005: Viscous Superlayer in a Reacting Turbulent Mixing Layer Cyrus K. Madnia, Reza Jahanbakhshi Direct numerical simulations (DNS) of reacting compressible shear layer have been performed to study some characteristics of the viscous superlayer (VSL). The VSL forms the outer sublayer of the turbulent/non-turbulent interface (TNTI), and is responsible for the transfer of vorticity from the high vorticity regions inside the turbulent region into the irrotational region by viscous diffusion. Budgets of the transport equation of enstrophy conditioned on the normal distance from the TNTI is used to define and detect the VSL. It is observed that in reacting and non-reacting compressible shear layers of current study, the conditional averages of the viscous diffusion and viscous dissipation terms start to deviate from zero slightly outside of turbulent region, whereas, the conditional averages of the other terms start to deviate from zero right at the interface. This is an indication of the presence of a viscous superlayer. A new method is used to find the thickness of the VSL. It is shown that while compressibility seems to have a small effect on the thickness of the VSL in the non-reacting cases, as the level of heat release increases the thickness of this layer decreases in reacting cases. [Preview Abstract] |
Monday, November 20, 2017 11:40AM - 11:53AM |
G29.00006: Density Effects on Incompressible Shear-Driven Mixing Layer Growth Jon Baltzer, Daniel Livescu Our preliminary simulations of shear-driven turbulent mixing layers involving two streams of fluids with different densities have revealed that the growth rates of mixing layer thickness are reduced when the density difference is increased, even in the absence of high-speed effects. To assess a wide range of densities, we have performed a suite of incompressible temporal Direct Numerical Simulations involving two miscible fluids, with Atwood numbers of up to 0.87. Large domains involving up to 6144 x 2048 x 1536 points provide accurate statistics of growth and budgets. For the variable density case, there is no unique definition of the layer thickness (e.g., momentum thickness may defined traditionally or on a per-mass basis). Yet, the thickness definition used can substantially affect the growth rate change due to density effects. We analyze the equations describing the growth rates and relate density effects to asymmetries that develop in the flow with increasing Atwood number. Most importantly, mixing layers are found to grow preferentially towards the lower-density stream, which has significant implications for the momentum balance. [Preview Abstract] |
Monday, November 20, 2017 11:53AM - 12:06PM |
G29.00007: ABSTRACT WITHDRAWN |
Monday, November 20, 2017 12:06PM - 12:19PM |
G29.00008: Turbulent shear layers in confining channels Graham Benham, Alfonso Castrejon-Pita, Ian Hewitt, Colin Please, Rob Style, Paul Bird The development of shear layers are ubiquitous in a wide range of situations, from diffusers, nozzles, turbines and ducts to urban air flow and geophysical flows. In this talk we present a simple model for the development of shear layers between flows that mix in confining channels. The model, comprising two plug flow regions separated by a linear shear layer, shows good agreement with both laboratory experiments and computational turbulence modelling (at a fraction of the computation time). Such efficient models, capable of capturing and exhibiting the main characteristics of the turbulent shear layers, are expected to be useful for both modelling and design purposes. We demonstrate the latter by showing how the model can be utilised to optimise pressure recovery in diffusers with non-uniform inflows. [Preview Abstract] |
Monday, November 20, 2017 12:19PM - 12:32PM |
G29.00009: Streamwise Lumley Decomposition of the Turbulent Round Jet Azur Hodzic, Clara M. Velte, William K. George Stream-wise Lumley decomposition was performed from data acquired using 2C-PIV, in order to decompose the far-field of a free turbulent axi-symmetric jet at a Reynolds number of 20 000. The equilibrium similarity scaling yields a homogeneous turbulent field leaving only the radial direction non-homogeneous. Fourier modes are used to decompose the flow in the new homogeneous stream-wise direction, while proper orthogonal decomposition (POD) is used to decompose the field in the inhomogeneous radial direction. The scaling allows spectral analysis and energy density spectra to be performed which together with Reynolds stresses are decomposed to reveal their modal building blocks and energy contributions. The results from the decomposition reveal that the number of modes needed to reconstruct the field varies with radial position. Explanations for these results will be presented and discussed. [Preview Abstract] |
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